
eInvoiceTool
E-Rechnungs-Studio.de
Invoice-Converter.com
Comarch Procure-to-Pay
Mustang Project
E-Invoice.Space
Offline validator for Polish FA(3)/KSeF e-invoices. Checks the FA(3) XSD plus 128 business rules grounded in the VAT Act and FA(3) brochure — catching what KSeF doesn't enforce before you submit. Windows desktop + Linux CLI, fully offline.
LayerStack’s Arm-based cloud virtual machines, powered by cloud-optimized CPU based on Arm architecture that deliver excellent cost-effective processing power, allowing you to easily complete the most demanding application development.

Website, pricing, platforms and company facts side by side.
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As answered by people managing KSeF Guard.pl and LayerStack Arm-based Cloud Server.
KSeF Guard.pl's answer
KSeF accepts structurally-valid invoices that still break substantive rules, and most validators only check structure. KSeF Guard adds 128 business/legal rules with VAT Act citations, runs 100% offline (invoice data never leaves your machine), produces bilingual audit-ready PDF/CSV/JSON reports, and validates whole folders in one pass — built for accounting offices working at volume. The free tier already includes all 128 rules.
KSeF Guard.pl's answer
As Poland's KSeF e-invoicing system makes FA(3) the mandatory invoice format (from 2026), a gap emerged: KSeF validates the XML schema, but the VAT Act and the FA(3) brochure impose substantive requirements the gateway doesn't enforce. Invoices can be accepted yet still be non-compliant — causing invoice-date shifts, VAT-period mismatches, or whole-batch rejections. KSeF Guard was built to catch those issues locally, before submission, with the legal basis spelled out for each one.
KSeF Guard.pl's answer
It validates Polish FA(3)/KSeF invoices fully offline against the FA(3) XSD and 128 substantive business rules — each traced to a documented source in the VAT Act or the official FA(3) brochure. In a 256-invoice test against the official KSeF test API, the system accepted 98 non-compliant invoices; KSeF Guard flags all 107 the API doesn't enforce (55 legal requirements, 52 best-practice/security checks). Every finding includes a bilingual PL/EN explanation, the exact XML location, a fix, and the legal citation.
KSeF Guard.pl's answer
Polish accounting offices (biura rachunkowe) and finance/AP teams that submit FA(3) invoices to KSeF at volume and need pre-submission certainty plus client-ready compliance reports. Also developers integrating FA(3) validation into CI/CD pipelines via the CLI.
KSeF Guard.pl's answer
A native Go validation core (using libxml2 for FA(3) XSD validation), a Tauri-based cross-platform desktop GUI, and a standalone command-line binary. All validation runs locally — there is no server component.
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